welding or spot welding is the generic term for electric welding processes in which ... shear strength by using WM Spot Welder Type MC 15 Welding machine.
THE EFFECT OF THICKNESS ON THE SHEAR STRENGTH OF SPOT WELDED AUSTENITIC STAINLESS STEEL Sham sul Baharin Jamaludin, Ooi Woei Ming, Mazlee Mohd Noor, Khairel Rafizi Pusat Pengajian Kejurut eraan Bahan Universiti Malaysia Perlis Taman Muhibbah 02600 Jejawi, Arau, Perlis
1. Introduction Electric welding by resistance [1, 2, 3, 4] is a process of assembly which is significantly used in several industrial fields of manufacture and maintenance (car industry, aerospace and nuclear sectors, electronics and electric industries). Resistance welding or spot welding is the generic term for electric welding processes in which the heat for welding is generated by the passage of welding current through a point of locally high electrical resistance created by pressure from electrode (spot and seam welding), or projections (projection welding), or by pressure applied across the whole area of the members being joined (resistance butt welding) [5]. Spot welding is the most common method of joining two strips of metal and has been studied for many years. To reduce weight and increase performance, the industry never stop to research and the spot welded joint has seen many changes [6]. Spot welds are crucial to the automotive industry. They make up a large percentage of the joints to hold an automobile together. The typical car body contains about 5000 spot welds joining a mixture of sheet metal material types and thicknesses [7, 8]. Tensile-shear strength testing is an important aspect of a weldability study in resistance spot welding. Intuitively, strength measurement of a welded specimen depends on the specimen size (width, overlap, thickness and length) and the spot weld (quality, size and location) [7]. This paper presents the effect of specimen thickness on the shear strength of spot welded austenitic stainless steel. 2. Experimental The material studied was austenitic stainless steel type 304 with a thickness of 1, 2 and 3 mm. The specimens were placed on each other as shown in Figure 1.
Figure 1: Spot welded specimen Spot welding was carried out to investigate the effect of specimen thickness on the shear strength by using WM Spot Welder Type MC 15 Welding machine. Figure 2 shows a process flow indicating a preparation of shear testing specimens. During welding process, welding current and welding duration are fixed and the selected thickness is 1
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mm 2 mm and 3 mm. Shear testing was carried out on GOTECT Universal Testing Machine (UTM). The tensile load was applied to determine the maximum strength on welded joint. The specimens for shear test do not have the regular dog bone shape. They consist of two sheets overlapping each other and a spot weld at the center of the overlapping area (Figure 1). Fracture surface was studied under optical microscope.
Figure 2: Process flow for specimen preparation 3. Results Figure 3 shows the bar chart indicating the maximum load of the different specimen thickness after shear test. In this test, the welding current and welding duration are fixed to 5 kA and 4 s respectively. It is indicated that the specimen thickness has influenced the weld joint. The specimen with 2 mm thickness has ability to support the highest maximum load (20,743.83 N) compare to 1 and 2 mm thickness. The quality of weld joint is very much influenced by the quantity of heat that generated at the interface during the welding process. The specimen with 1 mm thickness has the lowest maximum load (15,364.53 N), and it is expected that excess heat is generated at the weld joint to cause the expulsion and creates the larger heat affected zone around the weld joint. The specimen with 3 mm thickness has ability to support the lower maximum load (17,897.52 N) compare to the specimen with 2 mm thickness. In this case, the large thickness probably can transfer welding heat around the weld joint and reduces the quantity heat at the weld joint [8].
Figure 3: Bar chart of mean maximum load according to thickness of the specimens
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Figure 4 (a and b) shows fracture surface of the specimen with 2 mm thickness indicating plug or pull type failure that occurs by ductile shearing. This fracture behavior is associated with high value of maximum load. On the other hand, Figure 5 shows fracture surface of the specimen with 3 mm thickness indicating interface failure along the weld interface that frequently observed with low value of maximum load.
Figure 4: Fracture surface of specimen with 2 mm thickness after shear test (Optical micrograph 100X).
Figure 5: Fracture surface of specimen with 3 mm thickness after shear test (Optical micrograph 100X). References [1] [2] [3] [4]
Bouyousfi B, Sahraoui T, Guessasma S, Tahar Chaouch K, (2005), Effect Of Process Parameters On The Physical Characteristics Of Spot Weld Joints., Materials and Design, 28, (2007), 414-419. Vural M, Akkus A., On The Resistance Spot Weldability Of Galvanized Interstitial Free Steel Sheets With Austenitic Stainless Steel Sheets., J. Mater. Process Technol. (2004) 153, 1-6. Santos IO, Zhang W, Goncalves VM, Bay N, Martins PAF, Weld Bonding Of Stainless Steel., Int. J Mech. Tool Manuf. (2004), 1431-1439. Feulvarch E, Robin V, Bergheau JM, Resistance Spot Welding Simulation: A General Finite Element Formulation Of Electrothermal Contact Conditions., J. Mater. Process Technol. (2004), 153, 436-441.
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